New Evidence for 'Out of Africa' Origins

One of the biggest battles in human anthropology rages over whether modern humans descended from relatively recent emigrants from Africa or from several populations of early hominids, including Neandertals. Now a study of characteristic DNA sequences called "markers" in the Y chromosome adds support to the Out of Africa hypothesis.

When scientists sequenced DNA from the mitochondria of a Neandertal 4 years ago, they found that it was very different from that in living humans. The implication: We did not inherit mitochondrial DNA (mtDNA) from Neandertals, but from ancestors who swept out of Africa in the past 200,000 years and replaced all indigenous people they encountered (ScienceNOW, 10 July 1997).

But the backers of a dissident view--which holds that living humans are descended from several indigenous populations of the Old World--did not give up the fight. A recent analysis of fossils, they argue, shows that an archaic Homo erectus from Java shared key features with living Asians and early modern humans in Australia. They concluded that Asian H. erectus had passed on some of its DNA to modern Australians and Asians (Science, 12 January 2001, p. 293). Now, geneticists are storming this stronghold of multiregional evolution, as well.

As reported in this week's issue of Science, a team led by human population geneticist Li Jin of the University of Texas, Houston, and Fudan University in China took blood samples from 12,127 men in 163 populations in Asia, including China, Southeast Asia, and Siberia. They found that every one had inherited one of three markers indicating that their Y chromosome could be traced to forefathers who lived in Africa in the past 35,000 to 89,000 years. "We came to a simple conclusion," Jin says. "There are no mutations left [from archaic Asians]."

But because human genomes are a mosaic of genetic lineages, it is still possible that some of our nuclear DNA came from archaic humans who were not part of the recent migration out of Africa. "You can nail it down from the perspective of the Y and mtDNA, but that still leaves us at the doorstep of the nuclear genome," cautions evolutionary geneticist Michael Hammer of the University of Arizona in Tucson.